The present invention relates to a biological prosthetic heart valve intended as a replacement for patients with defective heart valves and more particularly to one that can be advantageously made using bovine pericardial tissue.
Biological tissue heart valves have evolved into several specialized designs to satisfy the on-going need of patients for a valve that will be free from structural failures and will last for the life of the adult. The primary focus of new designs for such valves has been to significantly increase the mechanical as well as the biological durability of the valve. In addition to the foregoing, these valves should be easy for surgeons to implant without any distortion and with consistent results, and the sewing ring design for an aortic valve should be compliant to accommodate both the calcific annulus as well as the annulus of a bicuspid valve.
Overall, tissue valves are still being sought that meet the following objectives: (1) low stresses at the coaptation surface of the leaflets in the closed position; (2) synchronous and symmetrical leaflet motion; (3) wrinkle-free leaflets at all phases of leaflet motion; (4) even alignment of the free margins of the tissue; and (5) hemodynamic efficiency from a trefoil stent design for the aortic position.
The present invention provides a bioprosthetic heart valve comprising a thin rigid outer frame which supports three elastic, laminated inner frames. Each inner frame comprises lamination in the form of thin crescent-shaped strips of elastic spring metal fastened together with one or more metal pins. A thin fabric covers over such inner frame structures for host tissue overgrowth and leaflet attachment. A tethered attachment between inner frames eliminates the possibility of leaflet tissue abrasion. Each free-standing inner frame provides a precise and consistent geometric positioning for one leaflet, and each is preferably designed with non-linear spring characteristics for symmetrical and synchronous leaflet motion. Such a laminated structure is able to decrease stresses at the commissure and coaptation zone without resulting in valve prolapse.
An aortic valve may have an outer frame that is trefoil-shaped in its horizontal aspect and scalloped in its axial aspect for supra-annular placement. The mounting diameter of the valve is generally measured as approximating a circle which includes the three commissure locations and goes through the three cusps of the trefoil. The outer frame is preferably made of metal that has been stiffened by increasing the section modulus through stretch-forming. To provide precision in positioning the three inner frames which support the stand-alone leaflets, slots are machined after the outer frame is formed. Both the inner and outer frames are covered with a polymeric fabric or sheet material for fastening purposes and to provide for tissue ingrowth as well known in this art, see U.S. Pat. No. 5,037,434.
An outer frame for a mitral valve is preferably circular in its inflow aspect and preferably has an oblong D-shape in the outflow aspect. Such a mitral valve may be designed to be implanted subannularly relative to the existing mitral valve so as to reside in the left atrium cavity. The valve is preferably designed so that the inflow plane of the valve housing will be tilted from 15 to 25xc2x0 from the outflow plane to obtain a better transition from such a circular inflow entrance to an oblong outflow exit. Bulges similar to the sinus of Valsalva will preferably be incorporated into the housing to reduce leaflet stresses during valve opening.
For such a subannular implantation, a bovine pericardial tissue skirt is preferably sewn to encircle the inflow end or nozzle, with the opposite edge of such skirt being attached to the left atrium to make an artificial floor. Polymeric elastomeric encircling cushions are preferably attached at both ends of the valve housing to absorb transient pressure loadings and provide a buttress for suture attachments.